Currently, the Federal Communications Commission (the “FCC”) is advancing location technology that enables emergency services to locate the geographic position of a mobile phone. This technology requirement has become known as Enhanced 911 or E911, for short. Different wireless communication systems or Radio Access Technologies (RATs) currently employ different location determination methods in order to effect E911 calls. For example, the Global System for Mobile Communication (i.e., “GSM”) standard and associated systems, although capable of supporting various location methods, typically support Uplink Observed Time Difference of Arrival (i.e., “UTDOA”) for location determination. On the other hand, the more recently deployed Universal Mobile Telephone Standard (i.e., UMTS) or 3GPP specification (3G) systems typically support Assisted Global Positioning System (“AGPS”) for location determination.
In certain geographic locations such as North America, however, early deployment of 3G systems may not support AGPS. This is due, in part, to the lack of current infrastructure and increased costs incumbent with AGPS. Thus, in order to still support E911 capability, cellular operators have proposed to use the already defined “Inter_RAT redirection procedure” set forth in section 25.331 of the 3GPP specification (3GPP TS 25.331) to move mobile stations or user equipment (UE) that do not support AGPS from Wideband Code Division Multiple Access (WCDMA) technology used by 3G to a different Radio Access Technology (RAT) that supports E911 location determination without needing AGPS. In particular, cellular operators propose moving UEs from 3G to GSM during an E911 call in order to locate UEs using UTDOA or another location methodology (which may include AGPS).
If a user initiates an emergency call while the user equipment is presently connected in a connected mode (e.g., the UE is in the middle of a packet session or is conducting a location update or routing area update) in a WCDMA cell, the user equipment will not send an RRC connection request, which is needed to initiate the redirection procedure according to the 3GPP standard (e.g., section 8.1.3.9 of the 3GPP TS 25.331 specification, V5.8.0, March 2004-03). Rather, the UE will use the existing connection and send a Non Access Stratum (NAS) message (e.g., a Connection Management Service Request) through an initial direct transfer message in accordance with the 3GPP specification. The result of following 3GPP specification procedures in this scenario, unfortunately, is that the 3G wireless network cannot redirect the user equipment to a GSM system (e.g., a different radio access technology), for example, to enable location determination by a GSM network. Therefore, it is desirable to ensure that a UE, which is initiating an emergency call when the UE is in WCDMA connected mode, initiate the redirection procedure to GSM in order to enable location determination of the UE.
Various aspects and features of the disclosure will become more fully apparent to those having ordinary skill in the art upon consideration of the following drawings and accompanying detail description wherein like reference numerals represent like operations or structure.